1. Field of the Invention
The present invention relates generally to a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to an apparatus and method for coding and decoding optimal (11,5) codewords.
2. Description of the Related Art
An IMT-2000 system, a future CDMA mobile communication system, transmits user data for a voice service, an image service and a data service, along with control data for performing the services. It is important to minimize errors occurring during transmission of such data in order to improve the quality of the services (QoS). To this end, error correcting codes for correcting data bit errors are used to minimize the errors occurring during transmission of the data. Since using the error correcting codes is aimed at minimizing the data bit errors of the transmission data, it is very important to use optimal error correcting codes.
Typically, linear codes are often used for the error correcting codes, because it is easy to analyze their capabilities. Hamming distance distribution for codewords of the error correcting codes can serve as a measure indicating the capability of the error correcting codes. The “Hamming distance” means the number of non-zero symbols in a codeword. That is, for a certain codeword ‘0111’, the number of 1's included in the codeword is 3, so that the Hamming distance is 3. The least value out of the hamming distance values is called a “minimum distance”, and an increase in the minimum distance of the codeword improves the error correcting capability of the codeword. In other words, the “optimal code” means a code having the optimal error correcting capability.
A reference, An Updated Table of Minimum-Distance Bounds for Binary Linear Codes (A. E. Brouwer and Tom Verhoeff, IEEE Transactions on information Theory, VOL 39, NO. 2, MARCH 1993), discloses an intercode minimum distance which depends on the input and output values of the binary linear codes to be optimal codes depending on the number of coded symbols generated by encoding input information bits.
The above reference discloses a (11,5) linear code of which the number of input information bits is 5 and the number of output coded symbols is 11, and its optimal code has the minimum distance of 4. Therefore, in using the (11,5) linear code, it is necessary to consider both using the optimal code having the minimum distance of 4 and creating the optimal code having the minimum distance of 4 while minimizing hardware complexity.